The invention disclosed and claimed herein deals with low to medium pressure, high temperature, all ceramic, air-to-air, indirect heat exchangers, novel ball joints, high load-bearing ceramic tube sheets, and connecting slip ring collars for ceramic tubes that are useful in such heat exchangers. Systems utilizing several heat exchangers or systems comprising heat exchangers are fabricated such that they provide more efficient heat transfer than has been possible heretofore.
The heat exchangers of this invention are not merely modified standard heat exchangers that are in use today, but are new and novel heat exchangers which require half the number of tube sheets of standard heat exchangers and which have outstanding efficiencies in operation, among other valuable benefits. Further, they have reduced tube to seal and tube sheet to shell leakage by a significant amount by use of the novel connector slip ring collars; novel ball joint assemblies and dense, interlocked, refractory tube sheets. The novel heat exchangers of this invention also reduce the tube to tube sheet leakage by a significant factor and reduce the tube sheet to tube shell leakage by a significant factor. The heat exchangers of this invention do not require air cooled tube sheets as does the prior art heat exchangers because of the novel low-heat conductive refractory shapes between the tube sheets and the shell of the heat exchanger. The entire manufacturing and assembly cost for tube sheets and tubes for these heat exchangers is reduced by over fifty percent as compared to the cost of manufacturing and assembly of the prior art heat exchangers. Further, the heat exchangers of the present invention do not lose any ability to replace individual tubes, nor do they lose the ability to use standard ceramic tubes.
Thus, it is one object of this invention to provide heat exchangers having the advantage of significantly reduced leakage of air. This reduced leakage allows for usage of higher pressures and essentially prevents mixing of dirty air with clean air during the operation of the heat exchangers.
It is yet another advantage of this invention to provide heat exchangers having the benefits of reduced cost of manufacturing and assembly, and it is still another object of this invention to provide heat exchangers which can be used with low to medium pressures and high temperatures where required.
Indirect, air-to-air heat exchangers are devices that are used to extract thermal energy from dirty heated gas and provide that thermal energy to a wide variety of diverse application such as heating clean ambient air, liquids, chemical processes, and similar uses. The source from which the extraction is made is usually waste gas of some kind, such as hot waste fumes from an industrial furnace or the like.
In general, conventional shell and tube heat exchangers utilize a series of tubes supported at their ends by what is known in the art as tube sheets. Ambient air flows through, or is forced through the tubes, and a cross flow of the hot gases, usually waste gases, is passed in a cross flow over the outside surface of the tubes to heat the air flowing through them. This is the concept of xe2x80x9cheat exchangexe2x80x9d. It will be noted that the applicant contemplates that the cross flow can be air and the material flowing through the ceramic tubes can be hot or waste gases.
Some conventional types of heat exchangers employ metal tubes which are welded at their ends to a supporting metal tube sheet. These metal heat exchangers are subject to deterioration from chemically corrosive or abrasive particles and further, they are subject to wide latitudes of expansion under operating conditions.
Conventional heat exchangers employing ceramic components have been used in the past in these types of adverse environments. One type of heat exchanger in this category employs a sponge or matrix made of ceramic material. The particulates in the waste fumes have a tendency to plug the matrix after a period of time thereby decreasing the efficiency and, in some instances, creating a fire hazard.
Yet another type of heat exchanger employs metallic springs pushing against one end of the ceramic tube or tube sheet in an effort to provide sealing engagement between the tube and the supporting tube sheet. Systems employing metal components to seal ceramics are subject to leakage problems since metal has a different rate of expansion than ceramic. In addition, the metallic components are still subject to deterioration under the above-mentioned adverse conditions in which these types of heat exchangers may be used. Also, in the likely event of power failure, the metallic components will fail when air side cooling stops.
Most of the known heat exchanger designs employ straight sided tubes which empty into plenums formed between the supporting tube sheets and the inner wall of the external housing or casing. The plenums are designed to carry the ambient air to other zones in the internal heat exchanger construction employing another set of tubes for passing the air back through the central chamber through which the heated waste fumes flow. Thus, the heat exchangers are normally stacked or otherwise fastened together to increase the operating flow length of both the ambient air and the waste gas and the flow of the ambient air between the plenums and tubes creates a pressure loss within the system. These pressure losses must be overcome by an increase in the horsepower of the fans for moving the ambient air in order to maintain a given velocity of the ambient air flow. These pressure losses also make it difficult to operate at high pressures, and consequently, the heat exchangers of the prior art are not operated at the higher pressures, or if attempts are made to do so, there is severe leakage. These pressure losses also make it difficult to maintain an air tight seal from the ambient air side to the gas side subsystem. The resultant leakage which may occur not only decreases the flow of the ambient air, but also allows air to flow into the fumes to reduce overall heat transfer efficiency. Also, there is an acute operating temperature loss in the heat exchanger with this type of arrangement. Air Side temperatures at operation of the prior art heat exchangers range from about 800xc2x0 F. to about 1200xc2x0 F., while the temperatures permitted by the use of the heat exchanger of the instant invention can range from 800xc2x0 F. to 2400xc2x0 F. Further, the pressures at operation of the prior art heat exchangers range from 0.25 psig to 250 psig, while the pressures permitted by the use of the heat exchanger of the instant invention can range from slightly above zero psig to 15 psig. Therefore, for purposes of this invention, what is meant by xe2x80x9clow to medium pressurexe2x80x9d are pressures in the range of slightly above zero psig to 15 psig, and what is A meant by xe2x80x9chigh temperaturesxe2x80x9d are temperatures in the range of 1800xc2x0 F. to 2800xc2x0 F.
One of the most egregious forms of inefficiency in heat exchangers occurs in the connections of the tubes to the tube sheets, wherein leakage is usually of a high volume. Further, these prior art connections are machined to decrease the tolerances and to prevent high leakage and this adds to the overall cost of such systems. In addition, the tube sheet itself is subject to expansion and when it expands, it expands in an uncontrolled manner which causes the tube sheet to move out of alignment, and thus causing more leakage. The prior art tube sheets also have a problem in that the tiles are manufactured such that they contain only one half of a tube opening in them and thus, that means many tube tiles have to be mortared together to obtain a tube sheet. Since these mortared joints microcrack under operating conditions, the more mortar joints that are used in a heat exchanger, the more leaks that occur in the tube sheets.
The heat exchangers of the prior art that are subject to many of the problems set forth above can be found in one or more of the following patents: U.S. Pat. No. 1,429,149, U.S. Pat. No. 1,974, ,402, U.S. Pat. No. 3,019,000, U.S. Pat. No. 3,675,710, U.S. Pat. No. 3,923,314, U.S. Pat. No. 4,018,209, U.S. Pat. No. 4,106,556, U.S. Pat. No. 4,122,894, U.S. Pat. No. 4,449,575, and U.S. Pat. No. 4,632,181, and the United Kingdom patents, 191,175, issued in January, 1923, and 2,015,146, issued in September of 1979.
One notable publication dealing with a flexible ball joint system for joining ceramic heat exchanger tubes to tube sheets is that entitled xe2x80x9cFLEXIBLE BALL JOINT SYSTEMxe2x80x9d, dated Apr. 11, 1995 in which there is shown a flexible ball joint system sold by Sonic Environmental Systems, Inc. wherein there is shown in an exploded view, a plug, a ball seal, a collar and a ceramic tube. This assembly has a slip surface between the tube and the ball seal. When the tube slides in and out of the seal due to thermal expansion, it does not pull the ball seal against the inner surface of the inner tube sheet tile or the ceramic tube. This results in a situation in which, when the tube sheets move during operation, the ball seals d not maintain their compression and leakage occurs. Further, without an attachment to the ceramic tube, the seal cannot move, either in a linear direction, or a lateral direction, both of which are requirements in a good sealing system.
Thus, there is needed a decidedly different heat exchanger to overcome the problems set forth above.
The invention disclosed and claimed herein deals with low to medium pressure, high temperature, all ceramic, air-to-air, indirect heat exchangers, novel ball joints and connecting slip ring collars for ceramic tubes that are useful in such heat exchangers, and systems comprising several heat exchangers or systems comprising heat exchangers that are fabricated such that they provide more efficient heat exchangers then has been possible heretofore.
More specifically, this invention deals in one embodiment with a low to medium pressure, high temperature, all-ceramic, air-to-air, indirect heat exchanger which comprises in combination (A) a novel, all-ceramic ball joint, said ball joint comprising a spherical body having an outer surface and an inner surface and having a near side and a tube side. The near side has a truncated face to form a flat surface on the near side. The spherical body has a first opening through it from the near side through the tube side. The tube side has a truncated face to form a flat surface on the tube side and the tube side has a second opening in alignment with and larger than the first opening to form a shoulder within the second opening which accommodates a ceramic tube in it. The outer surface of the spherical body is covered with a smooth, refractory ceramified, frit glaze.
(B) is an assembly comprising: (i) a tile; (ii) a closure ring; (iii) a plug, and (iv), at least one friable, crushable, alignment ring, wherein parts (i), (ii), and (iii) are ceramic bodies and wherein part (i) is a tile which forms part of a tube sheet. The tile has at least one round opening through it and has a plug side and a tube side and an inside surface. The tile has a discontinuous annular ring on the interior surface formed by the opening and near the plug side.
Part (ii) is a closure ring having a length essentially one-half of the width of the tile and it has a top surface, a bottom surface, a near end and a distal end wherein the top surface is bonded to the interior surface of the tile near the tube side of the tile such that the distal end of (ii) is essentially vertically aligned with the tube side of the tile. The part (ii) has an arcuate notch in the near end and in the interior surface. The arcuate notch is covered with a coating of a smooth, refractory ceramified frit glaze and mates with the spherical body outer surface.
Part (iii) is a plug. The plug has a plug top surface, a plug interior surface, a plug near end, a plug distal end, an opening through its center, and a horizontal midpoint, there is a discontinuous channel in the plug top surface to accommodate the discontinuous annular ring of the tile. The plug has a second arcuate note in the plug near end and in the plug interior surface. The second arcuate notch is covered with a smooth, refractory ceramified frit glaze and mates with the spherical body outer surface. The plug has a curved face at its distal end which begins at the plug interior surface and near the horizontal midpoint and ends at the plug distal end near the top surface. The closure ring and the plug provide a channelled opening between them at their near ends.
Part (iv) is a friable, crushable, alignment ring. The alignment ring is located in the channelled opening and Part C. are multiple ceramic heat exchanger tubes fitted with B. as set forth above.
Another embodiment of this invention is a heat exchanger as set forth just above, wherein, in addition, the ceramic tubes are fitted with B. on one end, and their opposite ends are connected together in an end to end configuration with a like-fitted ceramic tube using an all-ceramic connecting slip ring collar.
The ceramic tubes have an outside surface and the connecting slip ring collar has an outside surface and an inside surface. The connecting slip ring collar has an inside diameter such that the inside surface of the connecting slip ring collar is adaptable to and conforms with the outside surfaces of the ceramic tubes such that the connecting slip ring collar is closely, slidably mated with each of the ceramic tubes and supports such tubes. There is located within the connecting slip ring collar, and situated between the ends of the ceramic tubes, a friable, crushable, ceramifiable ring.
Still another embodiment of this invention is a novel, all-ceramic ball joint, said ball joint comprising a spherical body having an outer surface and an inner surface and having a near side and a tube side. The near side has a truncated face to form a flat surface on the near side. The spherical body has a first opening through it from the near side through the tube side and the tube side has a truncated face to form a flat surface on the tube side. The tube side has a second opening in alignment with and larger than the first opening to form a shoulder within the second opening to accommodate a ceramic tube in it. The outer surface of the spherical body is covered with a smooth, refractory ceramified, frit glaze.
Yet another embodiment of this invention is a novel all-ceramic ball joint assembly comprising the ball joint discussed supra in combination with (i) a tile; (ii) a closure ring; (iii) a plug, and (iv) at least one friable, crushable, alignment ring.
Further embodiments of this invention are a novel closure ring, a novel plug, and a novel alignment ring, all of which are useful in an all-ceramic ball joint assembly used in a unitary, ceramic tile.